Thin CA glue and a plastic square has always worked for me. After all the rib's are set Ifollow up with a medium thickness CA to make sure the strength is there. I'll use Titebond wood glue and lots of pins, weights and tape to glue the sheeting on. When joining the panels it's always 30 minute epoxy on all surfaces to be glues together.

Been building this way for many years and it has worked without failure.